1. Field of the Invention
The present invention relates to a touch-responsive circuit and to a data terminal or computer input device utilizing a plurality of such touch-responsive circuits.
2. Description of the Prior Art
The advent of low cost, large scale integrated circuit microprocessors paves the way for a new generation of consumer products built around such "CPU" (central processing unit) chips. But the commercialization of such consumer products depends on the availability of input devices that can provide a "man-machine interface" at correspondingly low cost. It is a principal object of the present invention to provide such a low cost man-machine interface.
The semiconductor industry now can mass produce very powerful data processors on monolithic substrates. These machines typically embrace a repertoire of 50 to 75 basic instructions and have addressing capability of up to 65,536 memory locations. Today, these CPU chips are predominantly used as components for data processing and test equipment manufacturers. But recent improvements in production techniques and yield have brought the volume prices of such CPU chips to well under $25 each. As a result, all of the components (e.g., processor, processing memory, data memory and memory interface) of a sophisticated data processor can be purchased for less than about $100. This price would permit mass production of inexpensive computerized home products, except for the man-machine interface.
Low speed alpha-numeric date input/output to a computer currently is implemented using electro-mechanical equipment such as a teletypewriter. Such equipment employs a complex mechanical typewriter-type keyboard together with a switch arrangement for producing a coded signal designating the selected key. Keyboard simplification generally has involved the use of opto-electronic switching and electronic circuitry to provide the data input codes. But even with these refinements, the cost is prohibitive for most consumer applications.
An object of the present invention is to provide a data input terminal of mechanical simplicity, advantageously having no moving parts. This may be achieved by employing touch-responsive circuits. Another object of the invention is to provide a novel touch-responsive circuit that can be logically enabled or disabled, thereby facilitating the use of such circuits in a scanned array of ohmic "touch" contacts.
Another shortcoming of prior art teletypewriter-type data terminals is that they are intended only for alpha-numeric data input. That is, each key designates a specific alphabetic or numeric character. Graphic input to a computer requires a totally different device, such as an optical document reader or a light-pen used in conjunction with a video display. Such graphic input devices are very costly and complex. It is another object of the present invention to provide a low cost data terminal which can be used for both alpha-numeric and graphic data input.